Tandem Thermo–electrochemical Strategy for Upcycling Waste Poly(ethylene terephthalate) into Value-Added Aniline Derivatives

Poly(ethylene terephthalate) (PET) is one of the most extensively used synthetic polymers. Despite its widespread use, the recycling of PET is limited to mechanical reuse or chemical depolymerization into low-value commodity chemicals. Herein, we report a method for upcycling PET through a tandem thermo–electrochemical transformation into high-value aniline derivatives, specifically p-aminobenzoic acid (PABA) and p-phenylenediamine (PPD). This strategy involves three cascade catalytic steps, including thermochemical zinc acetate-catalyzed PET glycolysis to bis(2-hydroxyethyl) terephthalate (BHET), thermochemical BHET ammonolysis to terephthalamide (TP), and electrochemical Hofmann (e-Hofmann) reaction of TP to PABA and PPD. Notably, the two thermochemical steps are highly efficient with 90.5% yield for glycolysis and 96.2% yield for ammonolysis, and only simple filtration was involved for intermediate purification, significantly minimizing the separation cost. Instead of using hazardous chemical oxidants for the Hofmann rearrangement, bromide-mediated e-Hofmann reaction utilized active bromine and base generated electrochemically to drive the rearrangements of TP. The developed protocol was tested for waste PET from a wide range of sources. A preliminary technoeconomic analysis estimated that the profit of this tandem thermo–electrochemical upcycling strategy would be $480/tonPET, outcompeting the traditional PET recycling process.